1. Field of the Invention
The present invention relates to the preparation of ethylene glycol having reduced aldehyde impurities content and improved ultraviolet transmission characteristics by treatment of already high purity distilled ethylene glycol (99% or higher) with strong acid cation exchange resin.
2. Description of the Prior Art
Ethylene glycol is a very important chemical of commerce which is usually prepared by reaction of ethylene oxide and water. A problem which has existed is that during the preparation procedure impurities such as aldehydes are formed which are difficult to separate from ethylene glycol and which cause problems in applications where very high purity is required, for example in the manufacture of fibers.
Both physical methods as well as chemical methods have been devised for the separation of aldehydes from ethylene glycol. U.S. Pat. No. 4,349,417, for example, proposes distillation in the presence of a alkali metal compounds as a purification procedure. This patent also refers to German Ausligeschrift No. 2,558,039 as teaching ethylene glycol purification using an ion exchange resin.
This German reference in turn refers to Wertschaft patent no. 43911 which teaches that aliphatic alcohols which contain more than 2% formaldehyde can be purified by converting the formaldehyde to formal using an acid catalyst followed by distillation of the impure, formal-containing alcohol. The patent states that at formaldehyde contents of less than 2% the amount of formaldehyde which is converted to the corresponding formal is so small that it is no longer possible to conduct the workup economically. Acid form ion-exchange resins are taught as suitable catalysts.
U.S. Pat. No. 4,358,625 teaches reducing oxygen-containing impurities by treatment with alkali metal borohydride.
U.S. Pat. No. 3,904,656 teaches treating a purge stream from an ethylene oxide stripper with a cation exchange resin Amberlyst A-15, an anion exchange resin Amberlyst A-21, and a carbon bed prior to recycle.
U.S. Pat. No. 4,560,813 teaches hydrolysis of alkylene oxide using a methylate anion--containing natural and recovery of the methylate anion by contact with a solid such as anion exchange resin.
U.S. Pat. No. 5,440,058 mentions treatment of aqueous streams with weakly basic ion exchange resins which have been reacted with a bisulfite salt in order to remove aldehyde impurities.
Despite the efforts of prior workers, further improvements in the removal of impurities such as aldehydes from aqueous ethylene glycol streams is important and desirable.
The presence of even very small amounts of aldehyde impurities ie. 2000 ppm by weight or less, has a deleterious effect on the properties of ethylene glycol and it is very important that economic procedures be provided to remove these materials or to convert them to a non-harmful form.